This invention relates to axial flow rotary separators for separating grain from a mass of crop material and more particularly to such a separator embodied in a combine and including threshing and cleaning sections.
Combines in which coaxial threshing and separating sections process grain delivered upwardly and rearwardly to them by the gathering and feeder units of a header are well known. It is also known to combine such units with a coaxial centrifugal fan disposed rearwardly (downstream) of the separator to provide cleaning air and to discharge straw ejected by the separator. However, in these combines, particularly where a coaxial fan is not included, it it typical to combine the axial flow rotary threshing and separating units with a cleaner having planar reciprocating screens, a cleaner design which has been conventional in threshing machines and combines using straw walker type separators for many years. Such cleaners and straw walkers, relying in part on gravity for control of the crop material being processed, are slope-sensitive and lose efficiency when the combine is operated on sloping ground. Attempts to include a rotary cleaning section in a rotary separator have usually been limited to a rudimentary revolving cylindrical drum.
In some existing combines having rotary separators there may be substantial centrifugal discharge of material over 360.degree. of arc from a rotating element, but typically such material is collected in the lower part of the separator by gravity and separate conveyors must be used to move the material to the next separating stage or to a cleaner. Other rotary separators already known rely for cleaning on centrifugal action produced by simple rotary motion plus aerodynamic means, or on the tumbling action produced by relatively slower rotation assisted in some cases by reciprocation of the revolving drum. When tumbling action is used to produce agitation, as in a revolving drum, only a part (the lower portion of the drum) of the total separating surface provided is in use at any one time.
The potential advantages of rotary separation and cleaning over conventional separators using straw walkers and reciprocating planar shoes in the cleaner are absence of slope sensitivity and inherently greater specific capacity in terms of rate of work per unit of separator volume. These advantages are not fully realized if the rotary elements are not rotated at such a speed that, through centrifugal action, their entire surfaces are in use at all times. And if a conventional reciprocating shoe type cleaner is used in conjunction with rotary threshing and separating, a disproportionately bulky cleaner is required to match the capacity of the rotary separating unit and the advantages of high specific capacity and slope insensitivity are both partially nullified.